In 2008 the National Highway Traffic Safety Administration (NHTSA) denied several petitions to create a new class of vehicles known as medium-speed vehicles (MSVs), which would have a top speed of 35 mph. The petitioners asked that MSVs be subject to a set of safety standards greater than those applied to low-speed vehicles (LSVs) but substantially less than those applied to conventional passenger cars. NHTSA denied the petition because, unlike LSVs, which are permitted to have a top speed of 25 mph and are intended for use in controlled, low-speed communities, MSVs travel in higher-risk traffic situations and should comply with all of the safety standards set for passenger cars. "While we appreciate the importance of environmental issues," the agency wrote in its denial, "NHTSA does not believe that it is necessary or appropriate to significantly increase the risk of deaths and serious injuries to save fuel by introducing a new class of motor vehicles that does not provide adequate safety protection."

However, just because NHTSA doesn't recognize MSVs doesn't mean they aren't allowed on public roads. States, not NHTSA, are responsible for regulating the operation of motor vehicles on the public roads and for handling titling and registration. There are nine states (Kentucky, Maryland, Minnesota, Montana, Oklahoma, Oregon, Tennessee, Texas and Washington) that specifically allow MSV use on specified portions of their public roads. Colorado enacted a law permitting the use of MSVs on the road once the U.S. Department of Transportation sets safety standards for them.

The table and map below show which roads MSVs are permitted on and their legally attainable speeds.